Body tie optimization for stacked transistor amplifier

ABSTRACT

A transistor stack can include a combination of floating and body tied devices. Improved performance of the RF amplifier can be obtained by using a single body tied device as the input transistor of the stack, or as the output transistor of the stack, while other transistors of the stack are floating transistors. Transient response of the RF amplifier can be improved by using all body tied devices in the stack.

CROSS REFERENCE TO RELATED APPLICATIONS—CLAIM OF PRIORITY

This application is a continuation of, and claims the benefit ofpriority under 35 USC § 120 of, commonly assigned and co-pending priorU.S. application Ser. No. 15/268,257, filed Sep. 16, 2016, “Body TieOptimization for Stacked Transistor Amplifier”, the disclosure of whichis incorporated herein by reference in its entirety. The presentapplication is related to U.S. application Ser. No. 15/268,297 entitled“Standby Voltage Condition for Fast RF Amplifier Bias Recovery” filed onSep. 16, 2016, the disclosure of which is incorporated herein byreference in its entirety. The present application is also related toU.S. application Ser. No. 15/268,229 entitled “Cascode Amplifier BiasCircuits” filed on Sep. 16, 2016, the disclosure of which isincorporated herein by reference in its entirety. The presentapplication is also related to U.S. application Ser. No. 15/268,275entitled “Gate Drivers for Stacked Transistor Amplifiers” filed on Sep.16, 2016, the disclosure of which is incorporated herein by reference inits entirety

The present application may be related to U.S. application Ser. No.14/945,323, entitled “Butted Body Contact for SOI Transistor”, filed onNov. 18, 2015, the disclosure of which is incorporated herein byreference in its entirety. The present application may also be relatedto Published US Application No. 2014/0171010 A1, published Jun. 19,2014, entitled “Semiconductor Devices with Switchable Ground-BodyConnection”, the disclosure of which is incorporated herein by referencein its entirety. The present application may also be related to U.S.application Ser. No. 15/078,930, entitled “Butted Body Contact for SOITransistor”, filed on Mar. 23, 2016, the disclosure of which isincorporated herein by reference in its entirety. The presentapplication may also be related to U.S. Pat. No. 8,987,792 B2, entitled“Merged Active Devices on a Common Substrate”, issued Mar. 24, 2015, thedisclosure of which is incorporated herein by reference in its entirety.The present application may also be related to U.S. Pat. No. 7,248,120,issued on Jul. 24, 2007, entitled “Stacked Transistor Method andApparatus”, the disclosure of which is incorporated herein by referencein its entirety. The present application may also be related toPublished US Application No. 2015/0270806 A1, published Sep. 24, 2015,entitled “Bias Control for Stacked Transistor Configuration”, thedisclosure of which is incorporated herein by reference in its entirety.The present application may also be related to Published US ApplicationNo. US 2014/0184336 A1, published Jul. 3, 2014, entitled “AmplifierDynamic Bias Adjustment for Envelope Tracking”, the disclosure of whichis incorporated herein by reference in its entirety. The presentapplication may also be related to U.S. Pat. No. 9,219,445 entitled“Optimization Methods for Amplifiers with Variable Supply Power”, issuedDec. 22, 2015, the disclosure of which is incorporated herein byreference in its entirety. The present application may also be relatedto U.S. Pat. No. 8,487,706 B2 entitled “Stacked Linear Power Amplifierwith Capacitor Feedback and Resistor Isolation”, issued Jul. 16, 2013,the disclosure of which is incorporated herein by reference in itsentirety. The present application may also be related to Published USApplication No. 2014/0184335 A1, entitled “Amplifiers Operating inEnvelope Tracking Mode or Non-Envelope Tracking Mode”, the disclosure ofwhich is incorporated herein by reference in its entirety. The presentapplication may also be related to Published US Application No.2014/0184337 A1, entitled “Control Systems and Methods for PowerAmplifiers Operating in Envelope Tracking Mode”, the disclosure of whichis incorporated herein by reference in its entirety.

BACKGROUND 1. Field

Various embodiments described herein relate generally to systems,methods, and apparatus for optimizing performance of radio frequency(RF) amplifiers that use stacked transistors.

2. Description of Related Art

Floating body silicon-on-insulator (SOI) transistors are limited inoperating voltage and power due to accumulated hot carriers which canincrease the electrical potential of the body region of the SOItransistors. Body tied SOI transistors have been shown to extend voltageand power handling capabilities when compared to floating body SOItransistors.

Floating body SOI transistors have shown non-conducting hot carrierdrift (e.g. magnitude of threshold voltage to decrease and the draincurrent to increase when in the non-conducting state) for drain tosource voltage (V_(DS)) larger than about 3.2 volts. Body tied deviceshave been shown to not suffer from this mechanism.

When a floating body transistor is conducting, a corresponding floatingbody effect (e.g., kink) can cause abrupt reduction of output impedanceof the transistor under moderate bias at various levels of drain tosource voltage of the transistor, which in turn, can reduce analog gainof the transistor and increase complexity of a corresponding devicemodeling. Body tied devices (transistors) suppress the reduction of theoutput impedance and extend the range of higher output impedance tohigher drain to source voltages.

Body ties on wide (large gate width) transistors with conventional(e.g., H-gate, T-gate or other) body tie structures become lesseffective in suppressing device degradations due to high resistance andincreased parasitic capacitance which mitigate the ability to controlthe floating body effects. In particular, conventional body tied devices(e.g. H-gate, T-gate or other) are less effective in suppressing suchdegradations for large transistor width and the added drain to gatecapacitance associated with conventional body tied devices can degradeperformance in applications where such transistors are used, such as,for example, radio frequency (RF) amplifier applications.

Although body ties can improve transistor voltage capability, otherperformance of the transistor, including ON state conduction and speed(e.g., f_(T), f_(MAX)), can be degraded. Such degradation can be due toseveral factors, such as an increase in parasitic capacitance, where theparasitic capacitance can be nonlinear; a larger layout area necessaryfor a body tied transistor; or, in some cases, limitations of designtools whose design rules prevent design of merged transistors with bodyties, therefore further increasing layout area.

For the above reasons, and in spite of benefits provided by body ties,traditional RF amplifiers using stacked SOI devices have not been fittedwith body ties. It should be added that, as known to person skilled inthe art, bulk CMOS devices inherently have body ties and therefore donot suffer from symptoms affecting SOI devices without body ties, suchas, for example, partially depleted and fully depleted CMOS deviceswithout body ties. Although capacitance reduction due to the absence ofbody ties in SOI devices can provide some performance advantages (e.g.,speed) over bulk CMOS devices, other performance parameters may suffer(e.g., voltage capability).

SUMMARY

According to a first aspect of the present disclosure, a circuitalarrangement is presented, the circuital arrangement comprising: atransistor stack configured to operate as a radio frequency (RF)amplifier, the transistor stack comprising a plurality of stackedtransistors comprising an input transistor for receiving an input RFsignal to the amplifier, and an output transistor for outputting anoutput RF signal that is an amplified version of the input RF signal;the transistor stack configured to operate between a supply voltagecoupled to the output transistor and a reference voltage coupled to theinput transistor, wherein at least one transistor of the plurality ofstacked transistors is a four-terminal transistor, and remainingtransistors of the plurality of transistors are three-terminaltransistors.

According to a second aspect of the present disclosure, a method formanufacturing a radio frequency (RF) amplifier is presented, the methodcomprising: providing a substrate comprising one of: a)silicon-on-insulator substrate, and b) a silicon-on-sapphire substrate;manufacturing, on the substrate, a transistor stack configured tooperate as a radio frequency (RF) amplifier, the transistor stackcomprising a plurality of series connected transistors comprising atleast one four-terminal transistor and a remaining three-terminaltransistor.

According to a third aspect of the present disclosure, a method forimproving a performance of a radio frequency (RF) amplifier ispresented, the method comprising: providing a plurality of floatingdevices; configuring the plurality of floating devices as a cascodedstack; based on the configuring, obtaining an RF amplifier having acharacteristic performance; replacing, in the cascoded stack, at leastone floating device of the plurality of floating devices with a bodytied device; based on the replacing, obtaining an RF amplifier having animproved characteristic performance; and fabricating the RF amplifierwith improved characteristic performance on one of: a)silicon-on-insulator (SOI) technology, and b) silicon-on-sapphiretechnology (SOS).

According to a fourth aspect of the present disclosure, a method forreducing a stack height of an RF amplifier is presented, the methodcomprising: providing a level of a voltage across a stack; providing awithstand voltage capability of a three-terminal device; based on thelevel of the voltage and the withstand voltage capability, determining aheight of the stack based on a required number of series connectedthree-terminal devices in the stack; replacing one or more of the seriesconnected three-terminal devices with one or more four-terminal devices;based on the replacing, reducing the height of the stack; andfabricating the RF amplifier with reduced stack height on one of: a)silicon-on-insulator (SOI) technology, and b) silicon-on-sapphiretechnology (SOS).

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of this specification, illustrate one or more embodiments of thepresent disclosure and, together with the description of exampleembodiments, serve to explain the principles and implementations of thedisclosure.

FIG. 1A shows a schematic representation of a three-terminal N-typeMOSFET transistor device.

FIG. 1B shows a schematic representation of a four-terminal N-typeMOSFET transistor device, where a fourth terminal can be used for a bodytie to any desired potential.

FIG. 1C shows a schematic representation of the four-terminal transistordevice of FIG. 2B, where the body is tied to a source of the transistor.

FIG. 1D shows a more detailed schematic representation of thefour-terminal MOSFET transistor device of FIG. 1B, including agate-to-source capacitance and a gate-to-drain capacitance.

FIG. 2 shows a schematic representation of a traditional transistorstack operating as an RF amplifier, where the transistor stack is formedby series connected three-terminal devices, and includes an input devicefor inputting an RF signal to be amplified, and an output device foroutputting an amplified version of the RF signal.

FIG. 3A shows a schematic representation of a transistor stack operatingas an RF amplifier according to an exemplary embodiment of the presentdisclosure, where the transistor stack is formed by series connectedthree-terminal devices and a series connected four-terminal inputdevice, a body of the input device being connected to an externalpotential.

FIG. 3B shows a schematic representation of a transistor stack operatingas an RF amplifier according to an exemplary embodiment of the presentdisclosure, where the transistor stack is formed by series connectedthree-terminal devices and a series connected four-terminal inputdevice, the body of the output device being connected to the source ofthe input device.

FIG. 4A shows a schematic representation of a transistor stack operatingas an RF amplifier according to an exemplary embodiment of the presentdisclosure, where the transistor stack is formed by series connectedthree-terminal devices and a series connected four-terminal outputdevice, the body of the output device being connected to an externalpotential.

FIG. 4B shows a schematic representation of a transistor stack operatingas an RF amplifier according to an exemplary embodiment of the presentdisclosure, where the transistor stack is formed by series connectedthree-terminal devices and a series connected four-terminal outputdevice, the body of the output device being connected to a source of theoutput device which is connected to a drain of an adjacent transistor ofthe stack.

FIG. 5A shows a schematic representation of a transistor stack operatingas an RF amplifier according to an exemplary embodiment of the presentdisclosure, where the transistor stack is formed by series connectedthree-terminal devices, a series connected four-terminal input device,and a series connected four-terminal output device, the body of theinput device and the body of the output device being connected to thesource of the input device and the source of the output devicerespectively.

FIG. 5B shows a more detailed schematic representation of the RFamplifier of FIG. 5A, including an impedance in the body ties.

FIG. 6A shows a schematic representation of a transistor stack operatingas an RF amplifier according to an exemplary embodiment of the presentdisclosure, where the transistor stack is formed by series connectedfour-terminal devices.

FIG. 6B shows a schematic representation of a transistor stack operatingas an RF amplifier according to an exemplary embodiment of the presentdisclosure, where the transistor stack is formed by series connectedthree-terminal and four-terminal devices.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

Throughout the present description, embodiments and variations aredescribed for the purpose of illustrating uses and implementations ofthe inventive concept. The illustrative description should be understoodas presenting examples of the inventive concept, rather than as limitingthe scope of the concept as disclosed herein.

Throughout the present description, the terms “transistor” and “device”are synonymous and can be used interchangeably.

Throughout the present description, a “three-terminal” transistor isreferred to as a transistor whose body is not tied to a potential and istherefore floating. A person skilled in the art would know that anotherexpression for a three-terminal transistor is a “floating transistor”.Therefore, the expressions “three-terminal” transistor and “floating”transistor are synonymous and are used interchangeably in the presentdescription.

Throughout the present description, a “four-terminal” transistor isreferred to as a transistor whose body is tied to a potential by way ofa body tie connection. A person skilled in the art would know thatanother expression for such transistor is a “body tied” transistor.Therefore, the expressions “four-terminal” transistor and “body tied”transistor are synonymous and are used interchangeably in the presentdescription.

Apparatus, and methods for making and using such apparatus, that provideall the benefits of conventional body tied devices, such as H-gate andT-gate structures for MOSFET devices, without some of the limitationsand degradations associated with those structures are described in theabove referenced U.S. application Ser. No. 14/945,323 and U.S.application Ser. No. 15/078,930, both entitled “Butted Body Contact forSOI Transistor”, whose disclosures are incorporated herein by referencein their entirety.

A body tie, according to various known embodiments, is implemented viaprovision of some additional structures to a semiconductor structurethat forms the transistor, which can result in a larger transistor withhigher capacitance (e.g. gate capacitance), and therefore, a slowertransistor. This is a main reason why traditionally RF amplifiers havenot been using transistors with body ties.

As known to a person skilled in the art, such body tie can be providedby “tying”, via a conduction path of a desired conductivity (e.g.resistivity), a body region of the transistor to a source region of thetransistor. Alternatively, the body tie can be provided as an opencontact for tying the body region of the transistor to any desiredexternal potential provided at the open contact, the open contact beingresistively connected to the body region of the transistor device via aconduction path of a desired conductivity.

The embodiments as described herein are exemplified by an N-type MOSFETdevice, as shown in FIG. 1A, used as a main conduction element of an RFamplifier. Such device can be part of a stack where a plurality of suchdevices are connected in series so as to operate as a cascode, as shownin FIG. 2. A person of ordinary skill in the art will readily apply theinventive concepts as disclosed herein to other types of semiconductordevices, such as a P-type MOSFET device. The embodiments, according tothe present invention, can also be applied to extended drain devices,such as laterally diffused metal oxide semiconductor (LDMOS) devices,and other gated transistors or devices.

According to various embodiments of the present disclosure, FET devicesT3 and T4 may include metal-oxide-semiconductor (MOS) field effecttransistors (FETs), complementary metal-oxide-semiconductor (CMOS) FETs,and particularly to MOSFETs and CMOSFETs fabricated onsilicon-on-insulator (SOI) and silicon-on-sapphire (SOS) substrates.

A person skilled in the art readily knows that an SOI MOSFET device(e.g. T3, T4 of FIG. 1A, 1B) can be formed in a thin layer of siliconwhich overlies an insulating layer of an SOI substrate. Accordingly, andas known in the art, the SOI MOSFET device can be referred to as athin-film SOI MOSFET, the thin-film referring to the thin layer ofsilicon. It should be noted that the various embodiments according tothe present disclosure which will be described below can be implementedin thin-film SOI MOSFET devices. A more detailed description of such SOIMOSFET device can be found, for example, in the above referenced U.S.application Ser. No. 14/945,323, U.S. application Ser. No. 15/078,930,and U.S. Pat. No. 8,987,792 B2, whose disclosures are incorporatedherein by reference in their entirety.

The MOSFET (FET) transistor T3, whose schematic representation is shownin FIG. 1A, is a three-terminal device, including a gate terminal, G, asource terminal, S, and a drain terminal, D. Due to its inherent smallersize, transistor T3 is a faster device and has traditionally been usedin RF amplification implementations. In contrast, the MOSFET transistorT4, whose schematic representation is shown in FIG. 1B, is afour-terminal device, including a gate terminal, G, a source terminal,S, a drain terminal, D, and a body terminal, B. In the exemplary casedepicted in FIG. 1B, the body terminal, B, is shown as an open terminalwhich can be tied to any desired (fixed) potential. In an exemplaryembodiment, the body terminal, B, can be tied to the source terminal, S,of the transistor T4, as shown in FIG. 1C.

The body tie provided to the device T4 can extend voltage and powerhandling capabilities of the device. According to the variousembodiments of the present disclosure, such semiconductor devices fittedwith a body tie structure can be used, for example, in radio frequency(RF) amplifiers, including, but not limited to, RF power amplifiers andcellular RF power amplifiers operating at various classes of operation,including, but not limited to, switching class D, E and F, saturatedclass B and C, and linear class A and A/B. A body tie used in one ormore transistors of a transistor stack operating as an RF amplifier,according to the various embodiments of the present disclosure, canimprove operating performance of the RF amplifier.

According to the various embodiments of the present disclosure, a stackof transistors operating as an RF amplifier can have a combination ofthree-terminal and four-terminal devices in the stack. According to anexemplary embodiment of the present disclosure, an input transistor ofthe stack can be a four-terminal device and all other transistors of thestack can be three-terminal transistors (e.g., FIG. 3A, FIG. 3B).According to another exemplary embodiment of the present disclosure, anoutput transistor of the stack can be a four-terminal device and allother transistors of the stack can be three-terminal transistors (e.g.,FIG. 4A, FIG. 4B). According to yet another exemplary embodiment of thepresent disclosure, an input transistor of the stack and an outputtransistor of the stack can be a four-terminal device and all othertransistors of the stack can be three-terminal transistors (e.g., FIG.5A, FIG. 5B). According to yet another exemplary embodiment of thepresent disclosure, all of the transistors of the stack can befour-terminal transistors (e.g., FIG. 6A). According to yet anotherexemplary embodiment of the present disclosure, any one or moretransistors of the stack can be a four-terminal device while remainingone or more transistors being three-terminal devices (e.g., FIG. 6B). Byusing a combination of three-terminal and four-terminal device in thestack of transistors, operating performance of the RF amplifier can beimproved.

Further clarification of the above embodiments according to the presentdisclosure, will be provided in the ensuing sections of the presentdisclosure with references to associated figures.

With further reference to the four-terminal transistor, T4, of FIG. 1Band FIG. 1C, the body tie structure can reduce the floating body effectspresent in the three-terminal transistor T3 of FIG. 1A, at the cost ofsome added parasitic capacitance (C_(SG)) between the gate and thesource of the transistor T4, as well as added parasitic capacitance(C_(DG)) between the gate and the drain of the transistor T4. Parasiticcapacitances (C_(SG), C_(DG)) are shown in FIG. 1D (as variablecapacitances, since corresponding capacitance value can change as afunction of the voltage applied to the transistor terminals), whichschematically represents transistor T4, including the body terminal(contact) which provides for a connection of a desired potential. Theperson skilled in the art readily knows the ill effects of suchparasitic capacitances in the performance of the transistor T4, which,amongst others, can reduce a switching speed of the transistor, as wellas reduce characteristic operating frequencies f_(T) and f_(MAX) of thetransistor T4 using the body tie. Due to the non-constant nature of theparasitic capacitances (C_(SG), C_(DG)), such capacitances can alsonegatively affect linearity of the transistor T4.

On the other hand, the four-terminal transistor T4 can exhibitperformance advantages when compared to the three-terminal transistorT3. Such performance advantages include, but are not limited to,improved control of majority carriers and electrical potential in thebody region of the transistor. When compared to a floating bodytransistor T3, the body tied transistor T4 can provide a higherbreakdown voltage, lower drain to source current (I_(DS)) in the OFFstate (non-conducting state) at elevated drain to source voltages(V_(DS)), less decrease in output impedance with increased V_(DS) in theON state (conducting state), and improved HCI (hot carrier injection)performance for RF applications.

Applicant of the present disclosure has found that careful constructionof a body tie structure used in one or more body tied transistors of astack operating as an RF amplifier, and careful layout of suchtransistors, can negate some of the ill effects of using body ties, andtherefore provide less total gate parasitic capacitance (sum of allcapacitances attached to the gate), less drain to gate capacitance (noincrease over floating body transistor), and higher f_(max) (due toreduced drain to gate capacitance). In addition, such RF amplifier canbenefit of the inherent characteristic benefits of the body tiedtransistors, including improved output impedance and breakdown voltage,which in turn, can provide improved performance of the RF amplifier,such as, for example, a higher peak power added efficiency (PAE),improved transient response, and improved RF swing absorptioncapability.

FIG. 2 shows a simplified schematic of a prior art stacked cascode (RF)amplifier (200). By way of example and not of limitation, the stackedcascode amplifier (200) can comprise a stack of FET transistors (T31,T32, T33, T34) that include a three-terminal input transistor T31,three-terminal cascode transistors (T34, T32, T32), and a three-terminaloutput transistor T34. An input RF signal, RFin, provided at a gateterminal of the input transistor T31 of the amplifier (200) is amplifiedby the amplifier (200). A corresponding amplified output RF signal,RFout, is provided at a drain of the output transistor, T34, and routedto an output terminal of the amplifier through a bypass capacitor C20.Bypass capacitors C10 and C20 can be used to decouple low frequency(e.g., DC) biasing voltages provided to the stack of transistors(transistor stack) from the RFin and RFout signals. A supply voltage,V_(CC), is provided to the drain of the output transistor, T34, throughan inductor, L20, and a reference voltage (e.g., GND) is connected to asource of the input transistor T31. Biasing voltages at nodes (V_(G4),V_(G3), V_(G2)) are provided to respective gates of the cascodetransistors (T34, T33, T32) via series resistors (R4, R3, R2). Biasingvoltage to the input transistor, T31, can be provided at the nodeV_(G1). Various biasing circuits to generate such gate voltages to theRF amplifier (200) are described, for example, in the above referencedU.S. Pat. Nos. 9,219,445, 8,487,706 B2, to Published US Application No.2014/0184335 A1, Published US Application No. US 2014/0184336 A1,Published US Application No. 2014/0184337 A1, and Published USApplication No. 2015/0270806.

A person skilled in the art would know that FET transistors (T31, T32,T33, T34) are configured as a four-stage cascode amplifier. Teachingsfrom other documents, such as the above referenced U.S. Pat. No.8,487,706 B2, whose disclosures is incorporated herein by reference inits entirety, further describe stacked cascode amplifiers and methods tominimize output signal distortion by way, for example, of biasing thevarious gates of the transistors within the stack. The person skilled inthe art may use these teaching for further specifics on multi-stagestacked transistors in a cascode configuration, where the stack of FETtransistors comprises a number of transistors different from four, suchas, for example, 2, 3, 5, 6, 7, 8 or more.

Although the amplifier (200) of FIG. 2 is shown to be powered by a fixedsupply voltage V_(CC), other configurations of the amplifier (200) wherethe supply voltage is variable can also be envisioned. In some exemplaryconfigurations, the supply voltage can be a voltage regulator, or aDC-DC converter. In further exemplary configurations, the supply voltagecan vary under control of an external control signal. In someconfigurations, the control signal can be a function of an envelopesignal of the input RF signal, RFin, or the output RF signal, RFout.Detailed description of biasing methods and apparatus for stackedtransistor amplifiers operating from a variable supply voltage can befound, for example, in the above referenced Published US Application No.US 2014/0184336 A1, Published US Application No. 2015/0270806 A1, andU.S. Pat. No. 9,219,445, the disclosures of which are incorporatedherein by reference in their entirety. A person skilled in the art wouldalso know of configurations where the supply to the amplifier is in theform of a current source instead of the exemplary voltage source (e.g.,V_(CC)) discussed in the present disclosure. The teachings according tothe present disclosure equally apply to such diverse supplyconfigurations. The exemplary case of a fixed supply discussed in thepresent disclosure should not be considered as limiting what theapplicant considers to be the invention. Furthermore, although anexemplary non-limiting case of a single ended RF amplifier configurationis discussed herein, the teachings according to the present disclosureequally apply to other amplifier configurations using stackedtransistors, such as, for example, differential configurations. Somesuch configurations are described in, for example, the above referencedPublished US Application No. 2014/0184335 A1, Published US ApplicationNo. US 2014/0184336 A1, and Published US Application No. 2014/0184337A1, whose disclosures are incorporated herein by reference in theirentirety.

As previously noted, although N-type MOSFETs are used in the exemplaryRF amplifier (200) of FIG. 2, a person skilled in the art wouldrecognize that other types of transistors such as, for example, P-typeMOSFETs, can be used instead or in combination with the N-type MOSFETs.Furthermore, a person skilled in the art will also appreciate theadvantage of stacking more than two transistors, such as three, four,five or more, provided on the voltage handling performance of theamplifier (200). This can for example be achieved when using nonbulk-Silicon technology, such as insulated Silicon-on-Sapphiretechnology. In general, individual devices in the stack (e.g. T31, T32,T33, T34) can be constructed using CMOS, silicon germanium (SiGe),gallium arsenide (GaAs), gallium nitride (GaN), bipolar transistors, orany other viable semiconductor technology and architecture known.Additionally, different device sizes and types can be used within thestack of devices.

The RF amplifier (200) may be used within mobile handsets for currentcommunication systems (e.g. WCMDA, LTE, LTE-CA, WiFi, etc.) whereinamplification of signals with frequency content of above 100 MHz and atpower levels of above 50 mW is required. Such amplifiers may also beused to transmit power at frequencies and to loads as dictated bydownstream splitters, cables, or feed network(s) used in deliveringcable television service to a consumer, a next amplifier in an RF chainat a cellular base station; or a beam forming network in a phased arrayradar system, and other. The skilled person may find other suitableimplementations for the present disclosure, targeted at lower (e.g.audio) frequency systems as well, such as audio drivers, high bandwidthlaser drivers and similar. As such, it is envisioned that the teachingsof the present disclosure will extend to amplification of signals withfrequency content of below 100 MHz as well.

With further reference to the amplifier (200) depicted in FIG. 2, thebiasing voltages at node (V_(G4), V_(G3), V_(G2)) are such that eachtransistor (T34, T33, T32, T31) of the stack is biased according to avoltage compliance of the transistor. In other words, a voltage acrossany two terminals (e.g., gate G4, G3, G2, G2, source S4, S3, S2, 51, anddrain D4, D3, D2, D1) of the transistor is within a safe operating rangeof the transistor. As failure of transistor can be a statisticalfunction of applied voltages across the transistors, even when suchvoltages are within the safe operating range, in some embodiments it maybe desirable to subject the transistors of the stack to same voltageranges so as to provide an equal life expectancy (e.g., mean time beforefailure) for each transistor of the stack.

With further reference to the RF amplifier (200) of FIG. 2, according toan exemplary embodiment, the gate biasing voltages at nodes (V_(G4),V_(G3), V_(G2)) can be configured to evenly distribute the voltageacross the transistor stack, V_(CC), amongst the stacked transistors(T34, T33, T32, T31). In other words, a drain to source voltage, V_(DS),of each transistor (T34, T33, T32, T31) of the stack is made to besubstantially equal to a quarter (¼) of the voltage provided by thesupply voltage V_(CC). This can be done, for example, as described inthe above referenced Published US Application No. 2015/0270806 A1, whosedisclosure is incorporated herein by reference in its entirety, bybiasing the gates of the transistors (T34, T33, T32) with respectivebiasing voltages at nodes (V_(G4), V_(G3), V_(G2)) equal toV_(CC)×¾+V_(GS), V_(CC)× 2/4+V_(GS), and V_(CC)×¼+V_(GS). According toother exemplary embodiment, unequal distribution of the voltage V_(CC)amongst the stacked transistors may be provided, while operating each ofthe transistors of the stack within its safe operating range.

A person skilled in the art would understand that during operation ofthe amplifier (200), an amplified RF signal at the drain of the outputtransistor (T34) can be at a voltage level substantially higher than theV_(CC) supply voltage. This means that if the gate voltage of the outputtransistor T34, as provided by the node V_(G4), is maintained at a fixedvoltage level, and therefore the source of T34 is maintained to a fixedvoltage level (e.g., V_(CC)×¾+V_(GS)), then the drain to source voltage,V_(DS), of the output transistor T34 can be subjected to higher voltageexcursions (including the RF signal), which can be beyond the tolerablevoltage range of the transistor. Unequal voltage distribution of thevoltage V_(CC) by way of gate biasing voltages, as discussed above, mayhelp to reduce stress exerted on the output transistor T34 due tounequal RF voltage distribution across the transistors of the stack, butmay not be sufficient.

Based on the above, it can be desirable to control the stress on theindividual transistors of the stack, due to unequal RF voltage divisionof the voltage at the drain of the output transistor T34 across thetransistors (T34, T33, T32, T31), which may subject any one of thetransistors to a voltage beyond the tolerable voltage range of thetransistor (e.g. close to or larger than its limit breakdown voltage).This can be accomplished by configuring the gates of the transistors(T34, T33, T32) of the stack to float via insertion of a gate capacitor(C4, C3, C2) as depicted in FIG. 2. The value of the gate capacitor ischosen so to allow the gate voltage to vary along (float) with the RFsignal at the drain of the corresponding transistor, which consequentlyallows control of the voltage drop (e.g., V_(DS)) across thecorresponding transistor, thus controlling the conduction of thetransistor in accordance to the voltage at its drain, for a moreefficient operation of the transistor. The voltage across thetransistors (e.g. V_(DS)) can therefore be equalized by choosing thecorrect combination of gate capacitor and gate bias voltage for each ofthe transistors. Teachings about this floating technique, also referredto as conduction controlling circuit, can be found in the abovereferenced U.S. Pat. No. 7,248,120, which is incorporated herein byreference in its entirety.

A person skilled in the art would know that performance characteristicof the RF amplifier (200) depicted in FIG. 2 is mainly a function of aperformance of the input transistor, T31. The input transistor T31operates as a transconductor that translates an input voltage of theRFin signal to a current that conducts through the transistor stack(T34, T33, T32, T31) and ultimately defines a voltage at the drain ofthe output device T34. It is therefore desirable to have an inputtransistor of the stack with good output impedance (V_(DS)/I_(DS)). As abody tied device can provide a smoother I_(DS) (drain-source current)versus V_(DS) response curve, and does not exhibit the well-known kinkwhich is characteristic of a floating body transistor, according to anembodiment of the present disclosure, the input transistor of the stackis a body tied device (e.g. T41 of FIG. 3A). As known to a personskilled in the art, such kink represents an abrupt decrease in outputimpedance of a floating transistor (V_(DS)/I_(DS)) and is not desirablein many RF applications as well as in lower frequency analogapplications.

FIG. 3A shows an exemplary embodiment according to the presentdisclosure where the input transistor, T41, of the RF amplifier (300A)is a four-terminal body tied device. The RF amplifier (300A) is similarin operation as the RF amplifier (200) described with reference to FIG.2, with the added benefits of using a body tied device as the inputtransistor T41. One such benefit is the lower OFF state current I_(DS)(leakage current) at elevated values of the drain to source voltageV_(DS) provided by the four-terminal input transistor T41 as compared tothe three-terminal input transistor of the RF amplifier (200) of FIG. 2.Moreover, the effective breakdown voltage (voltage V_(DS) at which thecurrent I_(DS) reaches a certain level) can be higher for the case ofthe four-terminal transistor, which means that the input transistor T41can allow for a higher input RF voltage swing while providing a sameoutput impedance, and therefore a higher output power of the RFamplifier (300A). Applicant of the present disclosure has found that theRF amplifier configuration of FIG. 3A can provide a higher PAE ascompared to the configuration of FIG. 2.

In the exemplary embodiment of the present disclosure depicted in FIG.3A, the body terminal B1 of the input transistor T41 of the RF amplifier(300A) is open, so as to allow any voltage to be tied to the body,including a fixed negative voltage. Alternatively, as shown in FIG. 3B,such body terminal may be tied to the source of the input transistorT41, the source being connected to ground.

As discussed above, the output transistor of the stack (e.g. T34 of FIG.2) can be subjected, during operation, to higher voltage excursions,which can be beyond the tolerable voltage range of the outputtransistor. Although the configuration of FIG. 2 provides some means tocontrol such higher excursions, it may be further desirable to provideincrease voltage withstand capability to the output transistor. Itfollows that according to another exemplary embodiment of the presentdisclosure, an RF amplifier (400A) of FIG. 4A, is provided with afour-terminal output device T44, which, as discussed above, inherentlycan withstand a higher voltage. The RF amplifier (400A) is similar inoperation as the RF amplifier (200) described with reference to FIG. 2,with the added benefits of using a body tied device as the outputtransistor T44, including increased voltage withstand capability.

In the exemplary embodiment of the present disclosure depicted in FIG.4A, the body terminal B4 of the output transistor T44 of the RFamplifier (400A) is open, so as to allow any voltage to be tied to thebody. Alternatively, as shown in FIG. 4B, such body terminal may be tiedto the source of transistor T44, the source being connected to the drainof the transistor T33.

FIG. 5A shows an exemplary embodiment according to the presentdisclosure where an input transistor T41, and an output transistor T44,of an RF amplifier (500), are both four-terminal devices. The RFamplifier (500) can be have the added benefits of a body tied inputdevice and a body tied output device as described with reference toFIGS. 3A/3B and 4A/4B.

It should be noted that resistivity of a body tie provided by acorresponding conduction path between the body of a device and its bodyterminal (contact) can be a design parameter. FIG. 5B showscorresponding body tie impedances (R41, R44). According to someexemplary embodiment of the present disclosure, such impedances (e.g.,resistances) can have a same value or different values.

As is well known to a person skilled in the art, when operating at highbias voltage and high RF power, the voltage of the body region of atransistor (e.g. transistor in any of the above described figures) of anRF amplifier can increase due to generated carriers. For a floating bodydevice, body potential increases, and can follow the high bias voltageand the high RF power with a relatively slow response (large timeconstant). This means that in response to fast changes in bias voltageand/or RF power, the floating body device reacts slowly and according toits relatively long time constant. Therefore, a transient response of anRF amplifier can be affected by presence of a floating device. On theother hand, the generated carriers in a body tied device are swept outvia the provided conduction path of the body tie which can thereforemaintain a potential of the body at a desired value as provided at thebody tie terminal, thus improving response of the device with respect tochanging biasing voltage and/or RF power. It follows that according toan exemplary embodiment of the present disclosure depicted in FIG. 6A,an RF amplifier (600A) is provided whose transistor stack comprises allfour-terminal devices for an improves transient response of the RFamplifier with respect to changing operating modes of the RF amplifierdefined by changes in biasing voltages and/or RF power.

With continued reference to the RF amplifier (600A) of FIG. 6A, aheight, N, of the stack of transistors can be of any value anddependent, for example, to the supply voltage V_(CC) and a withstandvoltage of the four-terminal devices (T41, T42 . . . , T4N). Asdiscussed above, an impedance (e.g., resistance) value (R41, R42 . . . ,R4N) associated to body ties of the transistors is also shown in thefigure. By virtue of using exclusively four-terminal devices, for agiven height of the transistor stack, the RF amplifier (600A) canprovide a faster transient response as compared to the RF amplifier(200) or any of the above described RF amplifiers having at least onefloating device (for a given height of the stack). Other benefitsrelated to using a body tied input transistor, T41, and a body tiedoutput transistor, T4N, as described with reference to FIG. 3A and FIG.4A equally apply to the configuration of FIG. 6A.

With further reference to the RF amplifier (600A) of FIG. 6A, due to thehigher withstand voltage capability of its body tied transistors, aheight of the stack for a given desired output voltage/power may bereduced, for a saving in power consumption of the RF amplifier ascompared to, for example, the configuration shown in FIG. 2. In otherwords, more of the lower withstand voltage floating transistors areneeded to distribute a same supply voltage, V_(CC), as compared to usingthe higher withstand voltage body tied transistors.

The teachings according to the present disclosure, therefore provide thetools to optimize performance of an RF amplifier using stakedtransistors by allowing a mixture of three-terminal and four-terminaldevices in the stack. Some such benefits can be readily understood basedon the above description. In other cases, design goals and correspondingRF amplifier layouts may result (e.g. through simulation) in differentstack configurations comprising a combination of one or morethree-terminal devices and one or more four terminal devices, as shownin FIG. 6B.

The exemplary non-limiting embodiment, according to the presentdisclosure, of an RF amplifier with stacked transistors in a cascodedconfiguration can be used, for example, in radio frequency (RF)amplifiers, including, but not limited to, RF power amplifiers andcellular RF power amplifiers operating at various classes of operation,including, but not limited to, switching class D, E and F, saturatedclass B and C, and linear class A and A/B.

Although the exemplary non-limiting embodiment described above are madewith respect to an RF amplifier using staked transistors, the teachingsof the present disclosure can equally apply to any other applicationswhere stacked transistors are used, including, for example, generalanalog circuits, power amplifiers (PAs), low noise amplifiers (LNAs),analog to digital converters (ADCs), voltage controlled oscillators(VCOs), and voltage reference circuits at frequencies ranging from DC to100 GHz and beyond.

It should be noted that although the various exemplary embodimentsaccording to the present disclosure are provided using an exemplary caseof an N-type SOI MOSFET, such exemplary case is provided mainly forclarity purposes. The various embodiments according to the presentinvention can be equally adapted to other transistor types and othertransistor technologies, especially where the source and/or the drainregions extend down to an insulating layer such as a “BOX” layer of anSOI device.

The term “MOSFET” technically refers to metal-oxide-semiconductors;another synonym for MOSFET is “MISFET”, formetal-insulator-semiconductor FET. However, “MOSFET” has become a commonlabel for most types of insulated-gate FETs (“IGFETs”). Despite that, itis well known that the term “metal” in the names MOSFET and MISFET isnow often a misnomer because the previously metal gate material is nowoften a layer of polysilicon (polycrystalline silicon). Similarly, the“oxide” in the name MOSFET can be a misnomer, as different dielectricmaterials are used with the aim of obtaining strong channels withsmaller applied voltages. Accordingly, the term “MOSFET” as used hereinis not to be read as literally limited to metal-oxide-semiconductors,but instead includes IGFETs in general.

As should be readily apparent to one of ordinary skill in the art,various embodiments of the invention can be implemented to meet a widevariety of specifications. Unless otherwise noted above, selection ofsuitable component values is a matter of design choice and variousembodiments of the invention may be implemented in any suitable ICtechnology (including but not limited to MOSFET and IGFET structures).Integrated circuit embodiments may be fabricated using any suitablesubstrates and processes, including but not limited to standard bulksilicon, silicon-on-insulator (SOI), silicon-on-sapphire (SOS), GaAspHEMT, and MESFET technologies. However, the inventive conceptsdescribed above are particularly useful with an SOI-based fabricationprocess (including SOS), and with fabrication processes having similarcharacteristics. Fabrication in CMOS on SOI or SOS enables low powerconsumption, the ability to withstand high power signals duringoperation due to FET stacking, good linearity, and high frequencyoperation (in excess of about 10 GHz, and particularly above about 20GHz). Monolithic IC implementation is particularly useful sinceparasitic capacitances generally can be kept low by careful design.

Voltage levels may be adjusted or voltage and/or logic signal polaritiesreversed depending on a particular specification and/or implementingtechnology (e.g., NMOS, PMOS, or CMOS, and enhancement mode or depletionmode transistor devices). Component voltage, current, and power handlingcapabilities may be adapted as needed, for example, by adjusting devicesizes, serially “stacking” components (particularly FETs) to withstandgreater voltages, and/or using multiple components in parallel to handlegreater currents. Additional circuit components may be added to enhancethe capabilities of the disclosed circuits and/or to provide additionalfunctional without significantly altering the functionality of thedisclosed circuits.

Applications that may include the novel apparatus and systems of variousembodiments include electronic circuitry used in high-speed computers,communication and signal processing circuitry, modems, single ormulti-processor modules, single or multiple embedded processors, dataswitches, and application-specific modules, including multilayer,multi-chip modules. Such apparatus and systems may further be includedas sub-components within a variety of electronic systems, such astelevisions, cellular telephones, personal computers (e.g., laptopcomputers, desktop computers, handheld computers, tablet computers,etc.), workstations, radios, video players, audio players (e.g., mp3players), vehicles, medical devices (e.g., heart monitor, blood pressuremonitor, etc.) and others. Some embodiments may include a number ofmethods.

It may be possible to execute the activities described herein in anorder other than the order described. Various activities described withrespect to the methods identified herein can be executed in repetitive,serial, or parallel fashion.

The accompanying drawings that form a part hereof show, by way ofillustration and not of limitation, specific embodiments in which thesubject matter may be practiced. The embodiments illustrated aredescribed in sufficient detail to enable those skilled in the art topractice the teachings disclosed herein. Other embodiments may beutilized and derived there-from, such that structural and logicalsubstitutions and changes may be made without departing from the scopeof this disclosure. This Detailed Description, therefore, is not to betaken in a limiting sense, and the scope of various embodiments isdefined only by the appended claims, along with the full range ofequivalents to which such claims are entitled.

Such embodiments of the inventive subject matter may be referred toherein individually or collectively by the term “invention” merely forconvenience and without intending to voluntarily limit the scope of thisapplication to any single invention or inventive concept, if more thanone is, in fact, disclosed. Thus, although specific embodiments havebeen illustrated and described herein, any arrangement calculated toachieve the same purpose may be substituted for the specific embodimentsshown. This disclosure is intended to cover any and all adaptations orvariations of various embodiments. Combinations of the aboveembodiments, and other embodiments not specifically described herein,will be apparent to those of skill in the art upon reviewing the abovedescription.

The Abstract of the present disclosure is provided to comply with 37C.F.R. § 1.72(b), requiring an abstract that will allow the reader toquickly ascertain the nature of the technical disclosure. It issubmitted with the understanding that it will not be used to interpretor limit the scope or meaning of the claims. In the foregoing DetailedDescription, various features are grouped together in a singleembodiment for the purpose of streamlining the disclosure. This methodof disclosure is not to be interpreted to require more features than areexpressly recited in each claim. Rather, inventive subject matter may befound in less than all features of a single disclosed embodiment. Thusthe following claims are hereby incorporated into the DetailedDescription, with each claim standing on its own as a separateembodiment.

The invention claimed is:
 1. A circuital arrangement comprising: atransistor stack configured to operate as a radio frequency (RF)amplifier, the transistor stack comprising a plurality of stackedtransistors comprising an input transistor for receiving an input RFsignal to the amplifier, and an output transistor for outputting anoutput RF signal that is an amplified version of the input RF signal;the transistor stack configured to operate between a supply voltagecoupled to the output transistor and a reference voltage coupled to theinput transistor, wherein at least one transistor of the plurality ofstacked transistors is a four-terminal transistor, and remainingtransistors of the plurality of stacked transistors are three-terminaltransistors, and wherein the at least one transistor comprises the inputtransistor.
 2. The circuital arrangement according to claim 1, furthercomprising one or more gate capacitors each connected between a gate ofa transistor of the plurality of stacked transistors except the inputtransistor, and a reference ground, wherein the each gate capacitor isconfigured to allow a gate voltage at the gate to vary along with aradio frequency (RF) voltage at a drain of the transistor.
 3. Thecircuital arrangement according to claim 2, wherein the one or more gatecapacitors are configured to substantially equalize an output RF voltageat a drain of the output transistor across the plurality of stackedtransistors.
 4. The circuital arrangement according to claim 1, whereinthe at least one transistor of the plurality of stacked transistorsfurther comprises the output transistor.
 5. The circuital arrangementaccording to claim 1, wherein the at least one transistor of theplurality of stacked transistors further comprises a transistor exceptthe output transistor.
 6. The circuital arrangement according to claim1, wherein the at least one transistor of the plurality of stackedtransistors comprises the plurality of stacked transistors.
 7. Thecircuital arrangement according to claim 1, wherein the plurality ofstacked transistors are metal-oxide-semiconductor (MOS) field effecttransistors (FETs), or complementary metal-oxide-semiconductor (CMOS)field effect transistors (FETs).
 8. The circuital arrangement accordingto claim 7, wherein the plurality of stacked transistors are fabricatedusing one of: a) silicon-on-insulator (SOI) technology, and b)silicon-on-sapphire technology (SOS).
 9. The circuital arrangementaccording to claim 7, wherein the plurality of stacked transistors areone of: a) N-type transistors, and b) P-type transistors.
 10. Thecircuital arrangement according to claim 1, wherein the supply voltageis a varying supply voltage.
 11. The circuital arrangement according toclaim 1, wherein a body of the at least one transistor of the pluralityof stacked transistors is coupled to a source of the at least onetransistor through an impedance of a corresponding body tie.
 12. Thecircuital arrangement according to claim 1, wherein a body of the atleast one transistor of the plurality of stacked transistors is coupledto a fixed reference potential through an impedance of a correspondingbody tie.
 13. An electronic module comprising the circuital arrangementaccording to claim
 1. 14. A method, comprising using of the electronicmodule of claim 13 in one or more electronic systems comprising: a) atelevision, b) a cellular telephone, c) a personal computer, d) aworkstation, e) a radio, f) a video player, g) an audio player, h) avehicle, i) a medical device, and j) other electronic systems.